In the recent past, to save well operator time and money, coiled tubing units have been used in more applications as a substitute for rigid tubing. The coiled tubing facilitates shorter trips into and out of the wellbore, thus reducing rig time required for given operations. One of the operations that are now desirable for use with coiled tubing units is to run casing or liner into a wellbore. When using a coiled tubing unit to accomplish this operation, it is desirable to have a running tool which has features which retain a grip on the liner or casing, regardless of whether the liner or casing is in tension or compression. It is also desirable to be able to transmit torque to the liner to facilitate its advancement or retrieval from the wellbore. Another desirable feature is to be able to be sure that once there has been release from the liner that it does not again accidentally become reattached to the running tool. These desirable features have been combined into the apparatus which is the subject of the present invention.
In the past, various tools for gripping and releasing have been employed. Various tools have had a feature for mechanical actuation of engagement but were designed in such a manner so that if the object to which the running tool or fishing tool was engaged was put into compression, there would be a release. Typical of such tools is that disclosed in U.S. Pat. No. 5,242,201, which illustrates mechanical engagement by physical displacement of the collets against an object to be retrieved but which as well indicates a design which will release when placed in compression. The fishing tool illustrated in U.S. Pat. No. 5,242,201 also indicates the state of the known art regarding transmission of torque through the collets. In the design illustrated in U.S. Pat. No. 5,242,201, the collets are reinforced with lugs so that they can better withstand transmitted torque. On the other hand, the apparatus of the present invention makes it possible to transmit torque without involving the collets, which differs from the prior designs which put a torsional stress through the collets. Since the design in U.S. Pat. No. 5,242,201 is for a fishing tool where release and relatching to a stuck object to be retrieved is desirable, it did not provide for a feature that positively prevents relatching once there has been release from the object. In running liner on coiled tubing, relatching would be undesirable because it is industry standard to be free from your liner prior to pumping cement. Upon releasing the running tool, the drillpipe and running tool are picked up to verify its release and then set back down and put in compression. Then cement is displaced down through the drillpipe and up around the outside of the liner. If cement is overdisplaced, the cement can get up around the running tool. If the running tool is not released, this could cause a problem.
Accordingly, the apparatus of the present invention represents an improvement over known devices. Particularly for operations involving running liner with coiled tubing, the apparatus provides a mechanism to retain the liner whether it is in tension or compression under application of fluid pressure to the tool, to transmit torque directly through the liner outside the collets, and to positively stay released from the liner once steps have been taken to deliberately release from the liner.